mechanics of materials qualifying...

Mechanics of Materials Qualifying Exam Study Material

The candidate is expected to have a thorough understanding of mechanics of materials topics. These topics are listed below for clarification. Not all instructors cover exactly the same material during a course, thus it is important for the candidate to closely examine the subject areas listed below. The textbook listed below is a good source for the review and study of a majority of the listed topics. One final note, the example problems made available to the candidates are from past exams and do not cover all subject material. These problems are not to be used as the only source of study material. The topics listed below should be your guide for what you are responsible for knowing. Suggested textbook: Fundamentals of Machine Elements, Hamrock, (McGraw-Hill) Topic areas:

Study Chapter 2 Chapter 5

Name ___________________________ Spring 2010

Qualifying Exam: Solid Mechanics

CLOSED BOOK Thisportionofthequalifyingexamisclosedbook.Youmayhaveacalculator.

Work3ofthe4problems.Beveryclearwhich3youwantgraded(seebelow).Itisnotacceptabletoworkall4problemsandhopethatthegraderspickoutthebestworkedthree.

Iwantproblems#____,#____,and#____graded.

Besuretoputyournameonallpapershandedin,includingthiscoversheet.

Name ___________________________ Spring 2010


CLOSED BOOK ReferenceFormulas

Thelawfortensorstransformation:

Iftwocoordinatesystems zyx and xyz arerelatedbythedirectioncosines: x,xcosl 1 ; y,xcosm 1 etcasshownintheTable1below,thenonecanwritethefollowingequationsfor

transformationsofcomponentsofthesymmetricsecondranktensor:

111111212121 2 nlanmamlanamalaa xzyzxyzzyyxxxx 222222222222 2 nlanmamlanamalaa xzyzxyzzyyxxyy 333333232323 2 nlanmamlanamalaa xzyzxyzzyyxxzz

212121212121212121

lnnlamnnmalmmla

nnammallaa

xzyzxy

zzyyxxyx

313131313131313131

lnnlamnnmalmmla

nnammallaa

xzyzxy

zzyyxxzx

323232323232323232

lnnlamnnmalmmla

nnammallaa

xzyzxy

zzyyxxzy

Table1Matrixofdirectioncosines

x y zx l1 m1 n1y l2 m2 n2z l3 m3 n3

In2Dcase,normalandsheartractions( and )arerelatedtocomponentsofstresstensorasfollows:

cossinsincos

cossinsincos

yxxy

xyyx

22

22 2

Theimpactfactor,theratioofthemaximumdynamicdeflection, max ,tothestaticdeflection, st ,is

stst

max h

211 ,wherehisheightfromwhichtheweightisdropped.

Name ___________________________ Spring 2010


CLOSED BOOK 1. Asolidshaftofcircularcrosssectionwithradius10mmissubjectedtoanaxialloadP=50.0kNand

torsionT.Foramaximumpermissibleshearingstress MPa330 calculatetheallowabletorqueT.

2. Whenaboltedconnectionfails,thethreadsmayfailineithershearortension.Estimatethenumberofthreads(i.e.,turnsofthenut)thatmustbeengagedinordertomakeeitherfailuremodeequallylikely.Assumethattheloadisdistributedevenlybetweenthethreadsandthattheboltandnutaremadefromidenticalsteel.Listyourassumptionsandindicatethetwopossiblefailuremodeswithasketch.Use.5inchstandardthreadasanexample.AmericanStandardThreadDimensionsareshown.

AmericanStandardThreadDimensions

Name ___________________________ Spring 2010


CLOSED BOOK 3. Alargethinplatecontainingasmallcircularholeofradiusaissubjectedtobiaxialloadingasshown

inthefigure.Determinethestressconcentrationfactor.

4. Thesteeringsystemofavehicleconsistsofasteeringwheel,ofasteeringcolumnwhichisashaftof

in.diameter,andofalinkagewhichgivesa20:1reductioninangularrotationbetweenthesteeringwheelandthetires.Eachofthefrontwheelscarries1,000lb.oftheweight,andthetiresareinflatedtoapressureof30psi.Ifthecoefficientoffrictionbetweenrubberandthegroundis0.6,calculatethemaximumstresssetupinthesteeringcolumnwhilethewheelsarebeingturned.(Tokeepthecalculationsimple,assumethatthecontactingregionbetweentireandgroundisacircleof6.5in.diameter,andthatthepressureoveritisuniformly30psi.)

in.diam.

Name ___________________________ Spring 2009


CLOSED BOOK 1. Thebuiltupbeamillustratedisclampedtogetherwithin.boltswithaspacingsasshown.If

eachboltcansafelyresistashearforceacrossitof400 ,whatistheboltspacingrequiredwhentheshearforce is10,000 ?

Mb

V

2

4 1

1

1

1

8 s

x

y

z

Name ___________________________ Spring 2009


CLOSED BOOK 2. A0o45o90orosetteisattachedtoapieceofisotropicandhomogeneousmaterialaccordingto

therecommendationoftherosettemanufacturerasshownbelow.ThismaterialhasaPoisson

ratioofwhichisNOTequalto0.285.StraingageAisalignedwiththex1axis,whilestraingageCisalignedwiththex2axisandgageBisat45

otothex1andx2axes.ThestraingagefactorofgagesA,BandCareSgA,SgBandSgCrespectively.Also,thetransversesensitivityratioofgagesA,BandCareKtA,KtBandKtCrespectively.ThestraingagefactorsandthetransversesensitivityratiosweredeterminedusinganisotropicandhomogeneousmaterialwithaPoissonratioof0.285.Ataparticularstateofloadingofthepieceofmaterialshowninthediagrambelow,thestrainsindicatedbygagesA,BandCwereeAi,eBiandeCi.

a. Whataretheindicatednormalstrainsofthematerialinthex1andx2directions?

b. Whatisthecorrespondingindicatedengineeringshearstrain12i?

c. Determinethecorrectednormalstrainsofthematerialinthex1andx2directions.

Name ___________________________ Spring 2009


CLOSED BOOK 3. AtpointP ,thematrixofcomponentsofstresstensor(withrespecttoaxes x1, x2 , x3 )isas

follows:

MPaij

5001003010101020

Determine:a. tractionvectoronaplanepassingthroughthispointandparalleltotheplane

1232 zyx ;b. normalandsheartractionsontheplane.

4. WithreferencetoarectangularCartesiancoordinatesystem,thestateofstrainatapointisgivenbythematrix

410210143

035

Whatisthechangeoftheanglebetweentwoinitiallyperpendicularlinesinthedirectionsof

321 eee 223 and 31 ee 32 emanatingfromthepoint?

Name ___________________________ Spring 2008 Qualifying Exam: Mechanics of Materials

CLOSED BOOK This portion of theThis portion of the qualifying exam is closed book. You may have a calculator. Work 3 of the 4 problems. Be very clear which 3 you want graded (see below). It is not acceptable to work all 4 problems and hope that the graders pick out the best worked three. I want problems #____, #____, and #____ graded. Be sure to put your name on all papers handed in, including this cover sheet.


CLOSED BOOK

Reference Equations The law for tensors transformation:

If two coordinate systems zyx and xyz are related by the direction cosines: x,xcosl 1 ; y,xcosm 1 etc as shown in the Table 1 below, then one can write the following equations for

transformations of components of the symmetric second rank tensor:

111111212121 2 nlanmamlanamalaa xzyzxyzzyyxxxx 222222222222 2 nlanmamlanamalaa xzyzxyzzyyxxyy 333333232323 2 nlanmamlanamalaa xzyzxyzzyyxxzz

212121212121212121

lnnlamnnmalmmla

nnammallaa

xzyzxy

zzyyxxyx

313131313131313131

lnnlamnnmalmmla

nnammallaa

xzyzxy

zzyyxxzx

323232323232323232

lnnlamnnmalmmla

nnammallaa

xzyzxy

zzyyxxzy

Table 1 Matrix of Direction Cosines

x y z x l1 m1 n1 y l2 m2 n2 z l3 m3 n3

In the 2-D case, normal and shear tractions ( and ) are related to components of stress tensor as follows:

cossinsincos

cossinsincos

yxxy

xyyx

22

22 2

The impact factor, the ratio of the maximum dynamic deflection, max , to the static deflection,

st , is

stst

h

211max , where h is height from which the weight is dropped.


CLOSED BOOK

1. With reference to a rectangular Cartesian coordinate system, the state of strain at a point is given by the matrix

410210143

035

What is the change of the angle between two initially perpendicular lines in the directions of

321 eee 223 and 31 ee 32 emanating from the point?

2. At point P , the matrix of components of stress tensor (with respect to axes x1, x2 , x3 ) is as

follows:

MPaij

5001003010101020

Determine:

a. The traction vector on a plane passing through this point and parallel to the plane 1232 zyx ;

b. The normal and shear tractions on the plane;


CLOSED BOOK 3. A cantilever beam has a Z section of uniform thickness for which

32 3 /thI y and 38 3 /thI z

and 3thI yz .

Determine the maximum bending stress in the beam subjected to a load P at its free end.

4. Consider two bars, one having a circular section of radius b, the other an elliptical section

with semi-axes a and b (b < a). For equal allowable shearing stresses, determine which bar resists a larger torque.

Name ___________________________ Summer 2007 Qualifying Exam: Mechanics of Materials

CLOSED BOOK

1. Two 50100 mm beams are glued together as shown. What is the required glue strength for both

cross-sections?

2. For the following matrix of components of stress tensor Pa810242420202

find the traction

vector on the plane shown.

2

13

x x

x

12

3

Hint: one of the ways to write down a normal to a plane is to take a vector product of any two vectors belonging to this plane

P 3m

P P

Glue joint

x

y

Cross-section 1 Cross-section 2


CLOSED BOOK

3. With reference to a rectangular Cartesian coordinate system, the state of strain at a point is given by the matrix

[ ] 410210121

012

=

What is the change of the angle between two initially perpendicular lines in the directions of 321 eee ++ 22 and 31 ee 62 emanating from the point?

4. In a typical application, a standard hex bolt and nut are used to clamp together two plates. As

the nut is tightened, a small rectangular strain gage rosette, mounted as shown on the bolt shank, registers strains that are converted into the following stresses (ksi):

0 = -9, 45 = 21, 90 = 29 From these results, the principal stresses are very nearly: 1, = 31.5 and 2 = -11.2

a. On a separate sheet, carefully sketch the Mohrs circle that depicts the two dimensional state of stress at the location of the strain gage rosette. On this Mohrs circle indicate the normal and shearing stresses in the 0, 45, and 90 degree gage directions. Label the axes.

b. Estimate the magnitude of the clamping force along the bolt axis, that is, in the 45 degree

direction.

It may be helpful to recall:


CLOSED BOOK

Name ___________________________ Fall 2006 Qualifying Exam: Mechanics of Materials

CLOSED BOOK

Thisportionofthequalifyingexamisclosedbook.Youmayhaveacalculator.

Work3ofthe4problems.Beveryclearwhich3youwantgraded(seebelow).Itisnotacceptabletoworkall4problemsandhopethatthegraderspickoutthebestworkedthree.

Iwantproblems#____,#____,and#____graded.

Besuretoputyournameonallpapershandedin,includingthiscoversheet.1. WithreferencetoarectangularCartesiancoordinatesystem,thestateofstrainatapointis

givenbythematrix

[ ] 410410123

035

=

Whatistheunitelongationinthedirection 321 eee 22 ++ ?


CLOSED BOOK

2. UsingStVenant'sprinciple,judgewhichofthethreeboundaryconditionswillresultin

approximatelysimilarstressstatessomewhatawayfromtheboundary:

(a) (b) (c)3. AtpointP ,thematrixofcomponentsofstresstensor(withrespecttoaxes x1, x2 , x3 )isasfollows:

[ ] MPaij

=

2001001001002005010050100

Determinetractionvectoronaplanewithunitnormal ( )333333 ,, passingthroughthispoint4. Atensiletestisperformedona12mmdiameteraluminumalloyspecimen( 330.= )using

a50mmgagelength.Whenanaxialtensileloadreachesavalueof kN16 ,thegagelengthhasincreasedby mm.100 .Determine(a)theYoung'smodulus;(b)thedecrease d indiameterandthedilatationofthebar

2

( ) 034 pxp =

2a

( )

= 2

2

0 143

axpxp

a

p0


CLOSED BOOK

This portion of the qualifying exam is closed book. You may have a calculator. Work 3 of the 4 problems. Be very clear which 3 you want graded (see below). It is not acceptable to work all 4 problems and hope that the graders pick out the best worked three. I want problems #____, #____, and #____ graded. Be sure to put your name on all papers handed in, including this cover sheet. 1. At a point in an isotropic elastic body the principal strains 1 , 2 , 3 are in the ratio 3:4:5;

the largest principal stress is MPa1401 = . Determine the values of principal stresses 2 and 3 if 30.= , GPaE 200= .

2. The inner surface of a hollow cylinder internally pressurized to 100 MPa experiences

tangential and axial stresses of 600 and 200 MPa, respectively. Make a Mohr circle representation of the stresses on the inner surface. What maximum shear stress exits at the inner surface?

3. A tensile test is performed on a 12-mm-diameter aluminum alloy specimen ( 330.= ) using

a 50-mm gage length. When an axial tensile load reaches a value of kN16 , the gage length has increased by mm.100 . Determine (a) the Young's modulus; (b) the decrease d in diameter and the dilatation of the bar


CLOSED BOOK

4. Figure shows a plastic beam having a box section, where the top plate is cemented in place. Determine the shear stress acting on the cemented joint for both designs. Is one design better than the other?

L/2

80,000 N

A B

L/2

cemented cemented

cemented

Design a Design b

NAME: _____________________ Fall 2004 Qualifying Examination

Subject: Mechanics of Materials

This portion of the qualifying exam is closed book. You may have a calculator. Work 3 of the 4 problems. Be very clear which 3 you want graded (see below). It is not acceptable to work all 4 problems and hope that the graders pick out the best worked three. I want problems #____, #____, and #____ graded. Be sure to put your name on all papers handed in, including this cover sheet. -------------------------------------------------------------------------------------------------------------------- Problem 1: A 45o rosette is used to measure strain at a critical point on the surface of a loaded beam. The readings are:

200=a ; 100=b ; 100=c for o

a 0= , o

b 45= , and o

c 90= .

Calculate the principal stresses and their directions.

Use GPaE 200= and 30.= -------------------------------------------------------------------------------------------------------------------- Problem 2: A hollow ( bR ernalint = , cRexternal = ) and a solid ( aR = ) cylindrical shaft are constructed of the same

material. The shafts are of identical length and cross-sectional area and both are subjected to pure torsion. Determine the ratio of the largest torques that may be applied to the shafts for b.c 41=

(a) if the allowable stress is a (b) if the allowable angle of twist is a .

-------------------------------------------------------------------------------------------------------------------- Problem 3: At point P , the matrix of components of the stress tensor (with respect to axes x1, x2 , x3 ) is as follows:

[ ]

=

35001000200100100100100

ij

Determine: (a) the traction vector on a plane passing through this point with unit normal ( )323332 ,, and (b) the normal and shear tractions on the plane.

NAME: _____________________ Fall 2004 Problem 4:

Consider a beam of rectangular cross-section ( )bh and length L . The beam is loaded by force T at the free end. Find the maximal normal stress n and shear n tractions along the glue

connection and the point(s) where they occur.

o45,21,1,5,10 ===== bhlL

Supplementary formulas:

The stresses at point ( )00 y,x of the beam of rectangular cross-section ( )bh and length L loaded by force T at the free end are as follows:

( )

zxx

I

yxM 00= , ( )0ySbI

Tz

zxy =

where

12

3bhI z = - cross-sectional moment of inertia

( ) ( )00 xLTxM = - bending moment at the cross-section with coordinate x0

( )

= 20

2

042

yhbySz

NAME: _____________________ Fall 2003 Qualifying Examination

Subject: Mechanics of Materials

This portion of the qualifying exam is closed book. You may have a calculator. Work 3 of the 4 problems. Be very clear which 3 you want graded (see below). It is not acceptable to work all 4 problems and hope that the graders pick out the best worked three. I want problems #____, #____, and #____ graded. Be sure to put your name on all papers handed in, including this cover sheet. -------------------------------------------------------------------------------------------------------------------- Problem 1: Determine the deflection at any point in the beam. Use singularity functions. -------------------------------------------------------------------------------------------------------------------- Problem 2: A rectangular plate is under a uniform state of plane stress in xy plane. It is known that the maximum tensile stress acting on any face (whose normal lies in the xy plane) is 75 MN/m2. It is also known that on a face perpendicular to the x axis there is acting a compressive stress of 15 MN/m2 and no shear stress. No explicit information is available as to the values of the normal stress y, and xy acting on the face perpendicular to the y axis. Find the stress components acting on the faces perpendicular to the a and b axes which are located as shown in the sketch.

2L/3 L/3

P

A B

k

15 MN/m2

x

y 15 MN/m2

yx

y

yx

y

300 x

a

b

NAME: _____________________ Fall 2003 Problem 3: A steel bar ( GPaE 207= ) of 6 cm2 cross-section and 6 m length is acted on by the indicated axially applied forces. Find the total elongation of the bar

-------------------------------------------------------------------------------------------------------------------- Problem 4: A 45o strain rosette is used to measure strain at critical point on the surface of a loaded beam. The readings are: 100=a , 50=b , 100=c for oa 0= ,

ob 45= ,

oc 90=

Calculate the principal stresses and maximum in-plane shearing stress if GPaE 200= , 30.= .

0.4 MN 0.5 MN 0.1 MN

3 m 3 m

Qualifying Exam Summer 2003 Mechanics of Materials

This portion of the qualifying exam is closed book. Work all problems. Problem 1: Strain rosette readings are made at a critical point on the free surface in a structural steel

member. The 60o rosette contains three wire gages positioned at oa 0= , o

b 60= , and

oc 120= . The readings are 190=a ; 200=b ; 300=c . Determine (a) the in-plane

principal strains and stresses and their directions, (b) the true maximum shearing strain. The

material properties are GPaE 200= and 30.= .

Problem 2: A right-angled-cantilevered bracket with concentrated load and torsional loading at the free end is shown in the figure. Using Castiglianos theorem, find the deflection at the free end in the z direction. Neglect transverse shear effects.

z x

P

T

y a

b

Solid round rod of Properties E, G, A, I, and J

1

2

3

Problem 3: Given the following stress field within a structural member,

( )[ ]222 yxbyax += abxyxy 2= ( )[ ]222 xybxay += 0== yzxz

( )22 xyabz += where a and b are constants. Determine, whether this stress distribution represents a

solution for a plane strain problem. The body forces are omitted.

Problem 4:

An aluminum rod in. in diameter and 48 in. long and a nickel steel rod in. in diameter and 32 in. long are spaced 60 in. apart and fastened to a horizontal beam that carries a 2000 lbf load, as shown in the figure. The beam is to remain horizontal after load is applied. Assume that the beam is weightless and absolutely rigid. Find the location x of the load and determine the stresses in each rod. (Youngs modulus: 6 2steelE 30 10 lbf in= and

6 2alE 10.3 10 lbf in= ).

.

. 48 in. 60 in.

x

32 in.

.2000 lbf

-in. diam aluminum rod

1/2-in. diam steel rod

Qualifying Exam Spring 2003 Mechanics of Materials

This portion of the qualifying exam is closed book. Work all problems. Problem 1: A 45 rosette is used to measure strain at a critical point on the surface of a loaded beam. The readings are: 100=a ; 50=b ; 100=c , for

oa 0= ;

ob 45= ; and

oc 90= . Calculate the principal stresses and their directions. Use GPaE 200= and

30.= .

Problem 2: Determine deflection y(x) as a function of x using singularity functions. Neglect the weight of the bar.

Problem 3: An aluminum core having a diameter di of 30 mm is placed within a tubular steel shaft having a diameter do of 50 mm. A flange is welded to the end of the shaft, and an axial force of 100 kN is applied. The shaft is 100 mm long. Find the deflection at the end of the shaft and the stresses induced in the aluminum and steel sections of the shaft. Assume that the moduli of elasticity are 2 x 1011 Pa for steel and 0.7 x 1011 Pa for aluminum.

y

x

L/3

w0

L/3 L/3

do di 100 kN

100 mm

Problem 4: Given the state of stress (in MPa) shown in the sketch. Determine the principal stresses and their directions and maximal shear stress.

40o

80

50

50

40o

80

50

50

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